Python to dynamically build JSON with sub arrays

Question

I can build JSON from simple dictionary {} and List [], but when I try to build more complex structures. I get '\' embedded in the output JSON.

The structure I want:

{"name": "alpha",
 "results": [{"entry1": 
        [
        {"sub1": "one"}, 
        {"sub2": "two"}
        ]
    }, 
    {"entry2": 
        [
        {"sub1": "one"}, 
        {"sub2": "two"}
        ]
    }
]
}

This is what I get:

   {'name': 'alpha',
    'results': '[{"entry1": "[{\\\\"sub1\\": \\\\"one\\\\"}, {\\\\"sub2\\\\": '
            '\\\\"two\\\\"}]"}, {"entry2": "[{\\\\"sub1\\\\": \\\\"one\\\\"}, 
    {\\\\"sub2\\\\": '
            '\\\\"two\\\\"}]"}]'}

Note the embedded \\. Every time the code goes through json.dumps another \ is appended.

Here's code that almost works, but doesn't:

import json
import pprint
testJSON = {}

testJSON["name"] = "alpha"

#build sub entry List
entry1List = []
entry2List = []
topList = []
a1 = {}
a2 = {}
a1["sub1"] = "one"
a2["sub2"] = "two"

entry1List.append(a1)
entry1List.append(a2)

entry2List.append(a1)
entry2List.append(a2)

# build sub entry JSON values for Top List
tmpDict1 = {}
tmpDict2 = {}
tmpDict1["entry1"] = json.dumps(entry1List)
tmpDict2["entry2"] = json.dumps(entry2List)
topList.append(tmpDict1)
topList.append(tmpDict2)

# Now lets' add the List with 2 sub List to the JSON
testJSON["results"] = json.dumps(topList)

pprint.pprint (testJSON)

You're embedding encoded JSON into a dict and then re-encoding the already-encoded JSON. If you want to "merge" JSON, just "merge" the dicts — Mark Nunberg
– Mark Nunberg, Commented Mar 31, 2016 at 23:36
Simply: build your data first in form of Pyhon dict or list, and finally convert it to JSON using json.dumps(data). JSON is not special data type, it is serialization method representing some data in form of a string. — Jan Vlcinsky
– Jan Vlcinsky, Commented Mar 31, 2016 at 23:40

Fiid · Accepted Answer · 2016-03-31 23:39:46Z

3

Look at this line:

tmpDict1["entry1"] = json.dumps(entry1List)

This is specifying that key entry1 have the value of the string output of converting entry1List to json. In essence, it's putting JSON in a JSON string, so it's escaped. To nest the datastructure, I'd go with:

tmpDict1["entry1"] = entry1List

Same with the other places. Once there is a tree of lists and dicts - you should only need to call json.dumps() once on the root container (either a dict or a list).

answered Mar 31, 2016 at 23:39

Fiid

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2 Comments

user3549628 Over a year ago

Ah! Makes sense - my usage pattern was wrong. Thank you for the clarification. I'll redo my approach.

user3549628 Over a year ago

Tested it out - worked great. So build the structure 1st and then use the json.dumps() function. thanks for the insight.

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